Peristaltic pumps are used in many medical and surgical procedures to circulate a patient's blood and are typically driven by electric motors. During some of these procedures, it is important that blood circulation remain substantially constant and uninterrupted. This is particularly true during cardiovascular surgery when a pump may be substituting for a patient's heart and may be circulating blood through a device which substitutes for the patient's lungs. Substantial interruption in such a case may result in injury, possibly including severe injury or death.
In cardiovascular surgery a patient's heart is often stopped and a bypass circuit provided comprising peristaltic pumps, reservoirs and oxygenators which bypass the patient's heart and lungs. Oxygen-poor or venous blood, is removed from the patient's circulatory system, passed through an oxygenator to oxygenate the blood, and returned to the patient's circulatory system to perfuse the patient with oxygenated, or arterial, blood.
Peristaltic pumps may become inoperative for a variety of reasons. For example, peristaltic pumps may lose power or fail due to any one of a number of well-known mechanical or electrical causes. Peristaltic pumps for use in cardiovascular surgery are typically provided with a hand cranking device. In the event that a pump becomes unable to continue pumping during a medical procedure for any reason, the pump rotor is turned by hand until a back-up pump is positioned. Where no back-up pump is available the pump rotor must be turned by hand for the duration of the medical procedure.
A serious problem in prior art pumps stems from the fact that peristaltic pump rotors may be rotated in either the clockwise or counterclockwise direction. Although relatively rare, cases have been reported where, in the transition from power to hand rotation, a pump user ("perfusionist") has rotated the pump rotor backwards. In other words, where a pump rotor was rotating in a clockwise direction before it became inoperative, the pump user manually rotated it in a counterclockwise direction or vice versa. Reversing the direction of the rotor rotation, correspondingly reverses the direction of blood circulation which can pull air into the peristaltic pump tubing. The perfusionist subsequently rotated the pump rotor in the forward direction; thus, injecting the air into the patient's circulatory system. Further, if reverse rotation is maintained, the patient may not be adequately perfused with oxygenated blood. Injecting air into a patient's circulatory system can result in severe injury or death. Further, these events can occur during times when other equipment is failing, further increasing the possibility, however remote, that the perfusionist may inadvertently turn the pump the wrong way.
Prior art pumps do not have the ability to detect rotor rotation reversal when the pump is not powered. Nor are prior art pumps designed to clearly and reliably indicate at a convenient location, when the pump power is off, the last rotation direction in which the rotor was travelling when the pump was operational. Some prior art pumps do have a manual reversing switch with labeled switch positions, but this switch's position can be changed by the perfusionist when power is off, so that it does not provide reliable indication of the last rotation direction. A perfusionist, therefore, generally must rely on memory and does not have a clear visual system when the pump is inoperational to help determine in which direction the pump rotor should be manually rotated to maintain adequate perfusion.